Method for contact between fluids

ABSTRACT

Precipitation of solids from a liquid is effected in a confined contact zone by passing the liquid downwardly through a rising stream of hot gas. A number of light weight spheres are confined within and freely movable throughout the zone. The upper and lower limits of the zone are defined by partitions each composed of a horizontal foraminous divider and an imperforate wall. The imperforate wall extends upwardly and outwardly from the divider and terminates at a wall defining the side limit of the zone. The velocity of the rising gas is highest as it passes through the divider and decreases upwardly therefrom. The gas causes the spheres resting on the divider to move upwardly and outwardly until the gas velocity is no longer capable of keeping the spheres in suspension whereupon the spheres fall downwardly along the side wall and imperforate wall scouring solids precipitated thereon.

United States Patent ['91 Gulyas et al.

1 1 METHOD FOR CONTACT BETWEEN F LUlDS [75] Inventors: James W. Gulyas; Charles Vydra,

both of Fort Saskatchewan. Canada [73] Assignee: Sherritt Gordon Mines Limited,

Toronto, Canada [22] Filed: July 3, 1973 [21] Appl. No: 376,266

Related US. Application Data [62] Division of Ser. No. 227.458 Feb. 18. 1972, Pat. No.

[56] References Cited UNITED STATES PATENTS 2,913,334 11/1959 Dean 75/119 3.219.324 11/1965 Williams et ul..... 55/91 17331161 5/1973 Bockmun 55/91 1 3,905,900 [4 1 Sept. 16, 1975 Primary Examiner-Thomas G. Wyse Assistant Examiner-Benoit Caste] Attorney, Agent, or FirmFrank 1. Piper; Arne l. Fors; James T. Wilbur 5 7 ABSTRACT Precipitation of solids from a liquid is effected in a confined Contact zone bypassing the liquid downwardly through a rising stream of hot gas. A number of light weight spheres are confined within and freely movable throughout the zone. The upper and lower limits of the zone are defined by partitions each com posed of a horizontal foraminous divider and an imperforate wall. The imperforate wall extends upwardly and outwardly from the divider and terminates at a wall defining the side limit of the zone. The velocity of the rising gas is highest as it passes through the divider and decreases upwardly therefrom. The gas causes the spheres resting on the divider to move upwardly and outwardly until the gas velocity is no longer capable of keeping the spheres in suspension whereupon the spheres fall downwardly along the side wall and imperforate wall scouring solids precipitated thereon.

2 Claims, 6 Drawing Figures PATENTEB 51975 3, 905 900 SHEET 1 [IF 2 PATENTH] SEP 1 6 I975 SHEET 2 0F 2 1 METHOD FOR CONTACT BETWEEN FLUIDS This application is a division of application Ser. No. 227,458 filed Feb. l8, I972 which issued as U.S. Pat. No. 3,771,657 on Nov. I3, 1973.

This invention relates to a method for establishing intimate contact between fluids and more particularly to a method for effecting contact between a gas and liquid passing countercurrently through a contact Zone in order to cause precipitation of solids from the liquid.

ln commercial operation in which a liquid is heated to distill off volatile components in order to cause precipitation of solids, the heating medium is frequently a gas. The liquid is heated by the gas in batch precipitators which consist of tanks through which the liquid and gas pass. Agitators are usually provided to keep the liquids in motion. After the reaction is complete, the resulting slurry is removed from the tanks and is processed for the separation of the solid precipitate.

The use of batch precipitators is subject to a number of disadvantagesv The solids which precipitate from solution frequently impair the performance of the precipitator. Many such solids have a tendency to adhere to the inside surfaces of the precipitator. The solids will quickly build-up on the side walls and agitators of the prccipitator necessitating periodic shut down and cleaning of the apparatus. Moreover, the precipitation of solids cannot be carried out on a continuous basis using a single precipitator. After the reaction between the liquid and gas is complete, the apparatus must be shut down to permit the liquid and solids to be removed.

In recent years, use has been made of elongated columns or towers for establishing contact between liquids and gasesv Such apparatus has the important advantages of permitting the gas-liquid contact to occur continuously. In operation, liquid is introduced as a stream near the top of the tower while the gas is simultaneously introduced into the bottom part of the tower. The liquid is allowed to fall within the tower and the gas travels upwardly and countercurrently to the descending liquid.

The problems caused by solids which precipitate from liquids passing through the towers described above are as serious as those caused by solids formed in batch precipitators. Vapours flowing upwardly through the towers whip countercurrently flowing liquid towards the interior wall of the tower and cause the liquid to flow downwardly along the interior wall. As a result of this so-called wall-effect", the solids precipitating from solution tend to coat the wall. These solids seriously impair the performance of the tower. If no steps are taken to remove these solids, the solids coating will increase in thickness and eventually bridge across the opening thereby blocking further flow of liquid and gas through the tower. Measures must be taken to remove the caked precipitate before the tower will again operate satisfactorily. The precipitate is customarily removed by shutting off the liquid and gas inlet valves, opening the tower to expose the compartments and cleaning the compartments using solvents or by other means. The cleaning operation is time-consuming and causes costly disruptions not only in the operation of the tower but in other operations dependent upon a continuous flow of liquid through the tower.

It is an object of the present invention to provide a method for precipitating dissolved constituents from liquids which method provides for continuous selfcleaning of precipitated solids from surfaces into which they come in contact.

A further object of the invention is to provide a method by which solids may be continuously precipitated from solutions in a confined contacting zone and continuously removed from the zone.

These objects are accomplished by a method which involves the mutual contact of gas and liquid in countercurrent flow in order to cause the precipitation of solids from the liquid. According to the method, upward flow of gas and downward flow of liquid are established through a confined gas-liquid contacting zone having a side limit defined by an interior wall and upper and lower limits defined by foraminous dividers. A plurality of light-weight spheres are maintained in the zone and are movable freely throughout it. The velocity of gas stream is adjusted such that the velocity is highest as the gas passes upwardly through each foraminous divider and decreases upwardly therefrom whereby the gas lifts any spheres in contact with the divider and carries them predominantly upwardly until the gas stream velocity is no longer sufficient to lift the spheres whereupon the lifted spheres move downwardly and outwardly thereby scouring precipitated solids from the interior wall.

Various features of the preferred embodiments of the invention are illustrated in the accompanying drawings in which:

FIGv l is an elevation of apparatus in which the method of the invention may suitably be carried out. The apparatus is shown partly cut away to expose two internal partitions;

FIG. 2 is a somewhat schematic vertical section of a portion of the apparatus;

FIG. 3 is a plan view on line 33 of FIG. 2;

FIG. 4 is another vertical section, partly schematic, showing the apparatus in operation; and

FIG. 5 and FIG. 6 (at the lower right hand corner of the first page of drawings) are perspective views of two different designs of partitions.

Like reference characters refer to like parts throughout the description of the drawings.

With reference to FIG. I, the apparatus consists of a hollow cylindrical tower 10 of a known type suitable for passing liquids therethrough in countercurrent flow to gases. At the upper end of the tower an inlet 12 is provided for the admission of liquid and at the top, an exit port 14 for the discharge of gas. At the lower end of the tower, an inlet I6 is provided for the admission of gas and at the bottom, a port 18 through which precipitated solids and liquids are discharged. A number of vertically spaced partitions 20 are positioned in the intermediate portion of the tower.

Feed liquid is introduced through upper inlet I2 and travels downwardly and countercurrently to a stream of gas introduced through lower inlet 16. As the liquid travels downwardly, the rising gas stream contacts and heats the liquid causing gases to evolve and solids to precipitate therefrom. Liquid together with precipitated solids discharge through outlet 18 at the bottom of the tower and vapour comprising gases introduced at lower inlet 16 and gases evolved from contact of the liquid feed with the rising gas stream are discharged through vapour outlet 14 at the top of the tower.

With reference to, FIGS. 2 and 3, the illustrated partition 20 includes a lower foraminous divider 22 disposed horizontally within the chamber and a solid imperforate frustoconical wall 24 which extends upwardly and outwardly from the divider and terminates at an outwardly turned circular edge 26 sandwiched between lower and upper sections 28a and 28b of the tower. Annular flanges 30 and 32 project outwardly from the outside wall of sections 28a and 2812 respectively and a number of bolts, two of which being illustrated and marked 34 pass through the flanges 30 and 32 to interconnect the sections. Access may be had to each partition by removing bolts 34 and separating the two sections which meet at the partition.

Partition and the next higher partition define the lower and upper limits of a gas-liquid contacting zone. A number of light weight spheres 36 are confined within the zone and are free to travel therein. The specific gravity of the spheres must be such that the rising gas, as it passes through the dividers is capable of elevating the spheres but the gas must not be travelling at a velocity which will cause flooding of the tower. The dynamic bed of spheres provides a large surface for contact between the descending liquid and rising gas for efficient heat and mass transfer from the gas to the liquid. In addition the spheres in the manner described below serve both to scour precipitated solids from inner walls contacted by the liquid and to remove solids deposited on the spheres themselves.

FIG. 4 illustrates the direction of travel of spheres 36 when buoyed upward by a rising stream of gas. The flow of gas is constricted at each partition and may only pass through divider 22. The velocity (v of the upward flow of gas is greatest at divider 22. As the gas rises above the divider its velocity (v,) decreases as does its carrying capacity for spheres 36.

The velocity of the gas introduced into lower inlet 16 is chosen such that the upward flow of gas as it passes through each divider is sufficient to lift any spheres resting on the divider. As the gas travels upwardly from each imperforate wall 24 its velocity must decrease sufficiently that it is no longer capable of keeping the spheres in suspension. The direction of travel of the spheres is indicated by the arrows. The large flow of gas centrally of the tower causes the spheres on the dividers to rise upwardly until the spheres reach the space above the upper edge of wall 24 at which time they travel radially outwardly and downwardly along the interior wall 37 and imperforate wall 24 and return to the divider. The arrows indicate the direction of travel of the spheres as a mass and not the path followed by individual spheres. Individual spheres will be deflected by other spheres and their paths will be erratic and unpredictable.

In general, the liquid falls straight down through each divider 22 and is not forced radially outwardly by the wall effect until it reaches a point somewhat below the divider. It is therefore unnecessary that the whole area of the interior tower surface between adjacent partitions be scoured by the spheres. The spheres need not be projected upward into the space where the liquid is falling directly downward from the upper partition. The rapid movement of the spheres may however splash some liquid against the upper portion of the interior wall between adjacent partitions. To inhibit build-ups of solids, it is desirable to coat this area as at 38 with material to which the precipitated solids do not readily adhere. A preferred coating material is polypropylene since precipitated solids adhere only slightly to such material and can be readily removed by simple methods. For example, where basic nickel carbonates are precipitated from an aqueous ammoniacal ammonium carbonate solution passing through the tower, nickel carbonates precipitated on surface coated with polypropylene can frequently be removed from the surface by simply washing the tower with water at a somewhat lower temperature than the ammonium carbonate solu tion normally passing through the tower.

The spheres effectively prevent precipitate from building up on the interior wall 37 and the frustoconical wall 24 but are not as effective in preventing buildup of precipitate on divider 22. Since any part of the foraminous divider serves as surface upon which precipitate can form, the surface area of the elements making up the divider should be as small as possible. Preferably therefore, the divider opening should be no smaller than that necessary to prevent the spheres from falling through the divider.

In cases where exceptionally sticky solids are precipitated from solution it may also be necessary to remove solids from the divider by other means. An apparatus which is found to be particularly suitable for this purpose is illustrated in FIG. 5. The apparatus is composed of a bar 40 connected to handle 42a and 42b. The bar together with spaced parallel rods 44 make up the fo raminous divider of each partition. Bar 40 is formed with apertures 46 slightly larger than the crosssectional area of rods 44. The rods pass through these apertures and are disposed at right angles to the bar. The rods are fastened beneath the lower edge of imperforate wall 47. Adjacent rods are disposed sufficiently closely to one another to prevent spheres from passing therebetween.

Bar 40 may be moved along rods 44 manually from outside the tower by means of handles 42 which extend outwardly through the tower wall. As the bar moves along the rods. solids deposited on the rods will be scraped away. Thus, build-up of solids on the divider can be eliminated by sliding bar 40 across the rods.

The slope of walls 24 (FIGS. 2, 3 and 4) and wall 47 (FIG. 5) should be sufficient to ensure that the spheres impinging on the walls prevent the build-up of precipitate. The slope depends on the material being treated and is determined experimentally but usually the angle between the wall and horizontal is within the range of from 35 to 50.

Satisfactory operation of the tower is dependent upon a number of factors. The slope of the imperforate wall of each partition must be such that the gas passing upwardly thereby causes the spheres to move predominantly in the required direction. The depth of spheres on each divider is important to satisfactory operation of the tower as is the diameter and specific gravity of the spheres. These factors vary according to the material being treated. the dimensions of the tower and operating conditions. Experiments are necessary to determine the conditions which result in satisfactory operation of the tower. For some applications, the partition illustrated in FIGS. 2 to 4 is suitable only in towers having a comparatively small internal diameter, generally 2 feet or less. Where towers of larger internal diameters are required for such applications, the towers may be provided with partitions of the construction illustrated in FIG. 6.

The partition illustrated in FIG. 6 designated generally 50. is made of a number of imperforate V-shaped ribs 52a, 52b and 520 disposed parallel to one another. The ribs open downwardly and are connected at their lower edges to a foraminous divider 54 which extends across the interior wall of the tower. An outer frustoconical wall 56 extends upwardly and radially out wardly to join with the interior wall of the tower. The divider is preferably composed of a number of thin parallel rods 58 spaced sufficiently closely together to prevent spheres 60 from passing therethrough. It will be understood that partition 50 may be used within a tower of any internal diameter and by suitable choice of the number of ribs incorporated into the partition, the requirements discussed above will be satisfied.

It is unnecessary that the tower of the invention have a circular internal cross-section. The crosssection may be rectangular or may be other shapes.

The operation of the tower is described with reference to the precipitation and separation of solids from a specific solution namely an aqueous ammoniacal ammonium carbonate solution containing dissolved nickel values in the form of basic nickel carbonates. The tower is packed with a number of polypropylene hollow spheres. Solution is fed into the upper zone of the tower and steam is injected into the lower zone. The condition of the stream is adjusted to maintain the spheres either in a so-called spouting state" or in a jumping state". Spouting" occurs when the spheres change their position in the dynamic bed but do not jump above the bed level whereas jumping occurs when the spheres change their position in a dynamic bed with such force that some spheres jump one inch or more over the bed level.

In the upper zone of the tower, ammonia and carbon dioxide are desorbed and no precipitation of nickel carbonate occurs. The spheres. partitions and column walls remain quite clean without extensive scaling. In the intermediate zone of the tower heavy precipitation and scaling of nickel carbonate occurs. In addition, large amounts of foam are produced above each partition. Movement of the spheres effectively prevents build-up of scale on the interior tower walls as well as the imperforate portions of the dividers.

The solution passing through the lower zone of the tower contains only minor amounts of ammonia and carbon dioxide and substantially all these volatile components come out of solution in this zone. The spheres do not move as widely in this zone as they do in the intermediate zone.

The gas should be travelling at sufiicient velocity to keep the spheres in motion in the lower zone in which the spheres tend to move only slightly and in the intermediate zone in which there is a large build-up of foam which resists movement of the spheres. The gas velocity is determined experimentally for each zone. For best performance of the column, the gas velocity is only slightly less than its flooding velocity.

Feed temperature has a marked effect on the boundaries between adjacent zones. For example, a roughly 25F. decrease from the standard feed temperature of 175F. shifts the boundary between the upper and intermediate zones one partition downv Thus adjustment of conditions in the three zones can be achieved, in part by varying the temperature of the solution at the feed inlet.

What we claim as new and desire to protect by Letters Patent of the United States is:

l. A process for treating an aqueous ammoniacal ammonium carbonate solution containing dissolved basic nickel carbonate in order to continuously precipitate said basic nickel carbonate and to remove ammonia and carbon dioxide therefrom which process comprises the following steps: introducing said solution downwardly through a substantially horizontal foraminous divider of a first partition into a confined gas-liquid contact zone having a side limit defined by an interior wall, an upper limit defined by said first partition and a lower limit defined by a second partition having a substantially horizontal foraminous divider, said dividers both being spaced apart from said interior wall, said first and second partitions also having imperforate frustoconical wall elements which slope upwardly and outwardly from the dividers and terminate at said interior wall; introducing a gas upwardly through the divider of said second partition into said zone such that upward flow of said gas and downward flow of said solution are established in the central region of said zone; maintaining the temperature of said gas at a sufiiciently high level to heat the solution within said zone and to cause ammonia and carbon dioxide contained in the lastmentioned liquid to evolve and basic nickel carbonate dissolved therein to precipitate; confining in said zone a plurality of light-weight spheres movable freely throughout the lower region of said zone; directing the downward flow of solution such that it passes wholly through each said divider, into the central region of the zone therebeneath and away from the area of the interior wall defining the upper region of said zone and adjusting the velocity of said gas below that at which said gas carries said solution upwardly and such that the velocity is highest as the gas passes upwardly through each said divider and the velocity decreases at a uni form rate upwardly therefrom and thereby lifts any spheres in contact with said divider and carries said spheres predominantly upwardly and towards the next higher said divider until the gas stream velocity is no longer sufficient to lift said spheres whereupon said lifted spheres cease their ascent predominantly in the lower region of said zone and well short of said next higher divider and move downwardly and outwardly of said central region thereby scouring the interior wall and the imperforate frustoconical wall elements.

2. A process for mutual contact of gas and an aqueous ammoniacal ammonium carbonate solution containing dissolved basic nickel carbonate in countercurrent flow in order to precipitate basic nickel carbonate and remove ammonia and carbon dioxide from said solution said process comprising the following steps: establishing upward flow of gas and downward flow of solution through a lower gas-liquid contacting zone and disposed immediately thereabove an upper gas-liquid contacting zone, said upper and lower zones being spaced apart by a first partition which also defines the lower and upper limits respectively of said zones and having lower and upper limits respectively defined by second and third partitions, said zones each having a side limit defined by an interior wall, each said partition having a substantially horizontal foraminous divider spaced apart from said interior wall and an imperforate frustoconical wall element which slopes upwardly and outwardly from the dividers and terminates at said interior wall; maintaining the temperature of said gas at a sufficiently high level to heat the solution within said zones and to cause ammonia and carbon dioxide contained in the last-mentioned solution to evolve and basic nickel carbonate dissolved therein to precipitate; confining in said zones a plurality of lightweight spheres movable freely throughout the lower region of said zones; directing the downward flow of solution such that it passes wholly through each said divider, into the central region of the zone therebeneath and away from the area of the interior wall defining the upper region of said zone and adjusting the velocity of said gas below that at which said gas carries said solution upwardly and such that the velocity is highest as the gas passes upwardly through each said divider and frustoconical wall elements 

1. IN A PROCESS FOR TREATING AN AQUEOUS AMMONIACAL AMMONIUM CARBONATE SOLUTION CONTAINING DISSOLVED BASIC NICKEL CARBONATE IN ORDER TO CONTINUOUSLY PRECIPITATE SAID BASIC NICKEL CARBONATE AND TO REMOVE AMMONIA AND CARBON DIOXIDE THEREFROM WHICH PROCESS COMPRISES THE FOLLOWING STEPS: INTO DUCING SAID SOLUTION DOWNWARDLY THROUGH A SUBSTANTIALLY HORIZONTAL FORMAINOUS DIVIDER OF A FIRST PARTITION INTO A CONFINED GAS-LIQUID CONTACT ZONE HAVING A SIDE LIMIT DEFINE BY AN INTERIOR WALL, AN UPPER LIMIT DEFINED BY SAID FIRST PARTITION AND A LOWER LIMIT DEFINED BY A SECOND PARTITION HAVING A SUBSTANTIALLY HORIZONTAL FORAMINOUS DIVIDER, SAID DIVIDERS BOTHE BEING SPACED APART FROM SAID INTERIOR WALL, SAID FIRST AND SECOND PARTITIONS ALSO HAVING IMPERFORATE FRUSTOCONICAL WALL ELEMENTS WHICH SLOPE UPWARDLY AND OUTWARDLY FROM THE DIVIDERS AND TERMINATE AT SAID INTERIOR WALL: INTRODUCING A GAS UPWARDLY THROUGH THE DIVIDER OF SAID SECOND PARTITION INTO SAID ZONE SUCH THAT UPWARD FLOW OF SAID GAS AND DOWNWARD FLOW OF SAID SOLUTION ARE ESTABLISHED IN THE CENTRAL REGION OF SAID ZONE: MAINTAINING THE TEMPERATURE OF SAID GAS AT A SUFFICIENTLY HIGH LEVEL TO HEAT THE SOLUTION WITHIN SAID ZONE AND TO CAUSE AMMONIA AND CARBON DIOXIDE CONTAINED IN THE LAST MENTIONED LIQUID TO EVOLVE AND BASIC NICKEL CARBONATE DISSOLVED THEREIN TO PRECIPITATE: CONFINING SAID ZONE AND PLURALITY OF LIGHT-WEIGHT SPHERES MOVABLE FREELY THROUGHOUT THE LOWER REGION OF SAID ZONE: DIRECTING THE DOWNWARD EACH FLOW OF SOLUTION SUCH THAT IT PASSES WHOLLY THROUGH EACH SAID DIVIDER, INTO THE CENTRAL REGION OF THE ZONE THEREBENEATH AND AWAY FROM THE AREA OF THE INTERIOR WALL DEFINING THE UPPER REGION OF SAID ZONE AND ADJUSTING THE VELOCITY OF SAID GAS BELOW THAT THE VELOCITY IS HIGHEST AS THE GAS PASSES UPWARDLY SUCH THAT THE VELOCITY IS HIGHEST AS THE GAS PASSES UPWARDLY THROUGH EACH SAID DIVIDER AND THE VELOCITY DECREASES AT A UNIFORM RATE UPWARDLY THEREFROM AND THEREBY LIFTS ANY SPHERES IN CONTACT WITH SAID DIVIDER AND CARRIES SAID SPHERES PREDOMINANTLY UPWARDLY AND TOWARDS THE NEXT HIGHER SAID DIVIDER UNTIL THE GAS STREAM VELOCITY IS NO LONGER SUFFICIENT TO LIFT SAID SPHERES WHEREUPON SAID LIFTED SPHERES CEASE THEIR ASCENT PREDOMINANTLY IN THE LOWER REGION OF SAID ZONE AND WELL SHORT OF SAID NEXT HIGHER DIVIDER AND MOVE DOWNWARDLY AND OUTWARDLY OF SAID CENTRAL REGION THEREBY SCOURING THE INTERIOR WALL AND THE IMPERFORATE FRUSTOCONICAL WALL ELEMENTS.
 2. A process for mutual contact of gas and an aqueous ammoniacal ammonium carbonate solution containing dissolved basic nickel carbonate in counter-current flow in order to precipitate basic nickel carbonate and remove ammonia and carbon dioxide from said solution said process comprising the following steps: establishing upward flow of gas and downward flow of solution through a lower gas-liquid contacting zone and disposed immediately thereabove an upper gas-liquid contacting zone, said upper and lower zones being spaced apart by a first partition which also defines the lower and upper limits respectively of said zones and having lower and upper limits respectively defined by second and third partitions, said zones each having a side limit defined by an interior wall, each said partition having a substantially horizontal foraminous divider spaced apart from said interior wall and an imperforate frustoconical wall element which slopes upwardly and outwardly from the dividers and terminates at said interior wall; maintaining the temperature of said gas at a sufficiently high level to heat the solution within said zones and to cause ammonia and carbon dioxide contained in the last-mentioned solution to evolve and basic nickel carbonate dissolved therein to precipitate; confining in said zones a plurality of lightweight spheres movable freely throughout the lower region of said zones; directing the downward flow of solution such that it passes wholly through each said divider, into the central region of the zone therebeneath and away from the area of the interior wall defining the upper region of said zone and adjusting the velocity of said gas below that at which said gas carries said solution upwardly and such that the velocity is highest as the gas passes upwardly through each said divider and the velocity decreases at a uniform rate upwardly therefrom and thereby lifts any spheres in contact with said divider and carries said spheres predominantly upwardly and towards the next higher said divider until the gas stream velocity is no longer sufficient to lift said spheres whereupon said lifted spheres cease their ascent predominently in predominantly lower region of said zone and well short of said next higher divider and move downwardly and outwardly of said central region thereby scouring the interior wall and the imperforate frustoconical wall elements. 